Digital cameras for capturing still images and movies are becoming increasingly popular. Many digital cameras allow very high quality images to be captured. Captured digital images may be processed by the digital camera and/or downloaded to a personal computer (PC) for processing. Capturing images in digital form offers many advantages over its analog counterpart. For example, capturing digital images avoids the step of chemical film processing, which involves the inconvenient procedure of leaving exposed analog film with a specialist. In addition, as most digital cameras capture images in a convenient format such as JPEG, BMP, TIFF or MPEG formats, the digital images may be easily transmitted electronically without conversion, to personal computers and/or peripherals such as printers.
An additional benefit of capturing images in digital form is that a user does not have to be particularly selective when capturing images. Unlike conventional analog film cameras, where exposed analog film is not available for further use, the memory of digital cameras can be used over and over to store images. If sufficient memory is not available, memory can be freed up either by deleting images from the memory or uploading images to a personal computer. This of course allows the user to capture a large number of digital images and later filter the digital images.
When capturing of a large number of images, it is useful for the images to be cataloged in some meaningful way. The software in most digital cameras automatically applies a filename to each captured image allowing the captured images to be identified. The filename may include an indication of the date of image capture, or some other detail concerning the image.
Image collections stored in PC filesystems include not only images captured using a digital camera but often also images from other camera sources. Some of these other images may be scanned copies of analog film prints, which carry perhaps a filename containing the date of scanning rather than the date of image capture, or a title based on an indexing scheme different from that used by the digital camera. In such cases, it is generally up to the user to view each image and manually re-title the filename if it is desired to maintain a searchable image collection. This requirement is particularly important where, for efficiency purposes, a graphic designer or magazine layout artist requires quick and easy access to stock images.
One common attribute applied to both analog film prints and digital images that is useful for indexing is the date stamp. When analog film prints bearing date stamps are scanned to convert them to digital form, the date stamps form part of the scanned images. In many instances, it is desired to detect the date stamps of scanned images so that this information may be used to catalog, identify and/or index the scanned images. Methods are known for extracting date stamps and other text from digital images using edge detection techniques.
For example, U.S. Pat. No. 5,852,678 to Shiau et al. discloses a method of detecting and rendering text in compound document images containing half tone tint regions and text and/or graphics embedded in the half tone tint regions. The method establishes a local average pixel value and effects discrimination based on a range of local averages by calculating gradients or second derivatives using edge information. Each pixel is categorized and is rendered according to its category.
U.S. Pat. No. 5,946,420 to Noh discloses a method of identifying text in a scanned image by first determining whether the image is comprised of mostly white and black pixels, and then sensing alternating left and ride side edges using a vertical/step test function.
U.S. Patent Application Publication No. US2003/0026480 to Karidi et al. discloses a method and apparatus for detecting text in an image that employs intensity troughs and local ramp detection. The image is segmented into text and non-text portions in order to provide higher-quality reproduction by processing the text and non-text portions in different manners. Relatively sharp edges in the image are used as a text criteria.
Although the above references disclose methods for determining the location of characters in digital images, the disclosed methods are generally only suitable in situations where excellent character edge information is available. Often, however, the characteristics of date stamp characters vary significantly depending on whether the image is captured using a digital camera or is a scanned analog film print. For instance, images captured using digital cameras typically have clean edges and are high in saturation. On the other hand, scanned images tend to be noisy and have tainted color due to the translation process. Adding to the difficulties is the fact that date stamps are generally meant to be viewed by the human eye and not by machine. As a result, date stamp character resolution is often low, the color of the date stamp characters is not standardized, the date stamp characters are not necessarily solid colors especially for scanned analog film prints, and the size and font of the date characters can vary significantly. These factors can make character sets and particularly date stamps difficult to locate in images.
It is therefore an object of the present invention to provide a novel system and method for locating a character set, such as for example a date stamp, in a digital image.